Crude Rhizopus oryzae lipase was immobilized on different supports. The CaCO3 was selected as the most suitable adsorbent preserving the catalytic activity almost intact and offering maximum adsorption capacity. Immobilization enhanced the thermo-stability of lipase. Enzymatic esterification between oleic acid and butanol at 37 degreesC with shaking (200 rpm) was realized in two systems: n-hexane and solvent-free system. The product of this reaction, 1-butyl oleate, is useful as a diesel additive, a polyvinyl chloride plastisizer, a water-resisting agent and in hydraulic fluids. The influence of reaction conditions such as the amount of lipase used, the presence of water and the substrate concentrations on I-butyl oleate synthesis were investigated. The optimal conditions for the esterification reaction in a solvent-free system were 60 IU of immobilized lipase and a molar ratio of oleic acid to butanol of 1:1. The reaction could be performed in presence of hexane and the highest conversion percentage (73%) was obtained with 60 IU of immobilized lipase and substrate concentrations of 0.1 M each. Immobilized lipase could be repeatedly used for six cycles without a decrease of synthesis activity. The immobilized R. oryzae lipase exhibited long-chain fatty acids specificity similar to that shown for the free lipase. Besides, the former lipase synthesizes more efficiently the short-chain alcohols than the longer-chain. (C) 2004 Elsevier Inc. All rights reserved.